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Uncertainty Sets Limits On Quantum Nonlocality
An anonymous reader writes "Research in today's issue of the journal Science helps explain why quantum theory is as weird as it is, but not weirder. Ex-hacker Stephanie Wehner and physicist Jonathan Oppenheim showed that the Heisenberg Uncertainty Principle sets limits on Einstein's 'spooky action at a distance.' Wired reports that the discovery was made by 'thinking of things in the way a hacker might' to uncover a fundamental link between the two defining properties of quantum physics (abstract, supplement). Oppenheim describes how uncertainty and nonlocality are like coding problems, enabling us to make a quantitative link between two of the cornerstones of quantum theory."
I want to believe in quantum physics, but I'm not sure.
Living With a Nerd
Lolwut?
I think you run into issues when you start thinking about non-coding problems from a coding perspective. The universe doesn't behave like a computer as much as you might like it to.
That the universe is actually a computer.
Definitely not a link to the full article here [Not-PDF warning].
Heck, they even hinted at Gödel. Why not throw in Monty Hall too... wait, they did.
Set your phasers on "funky"!
Since the Earth is a 10-million-year program (HHGG) then it makes sense the Universe would be a computer!
Deep thought!
Encryption: I may not agree with what you say, but I will defend your right to encrypt it...
Locality is the only thing stopping me from concluding the universe is entirely deterministic and free will doesn't exist.
describes how uncertainty and nonlocality are like coding problems,
In that case, I guarantee there is a bug.
Qxe4
Okay, I get it, text shadow is the new 'thing' on the internet. But seriously, it makes your article harder to read. There is a time and a place people. And that time and place isn't everywhere all-the-time.
Okay, rant time.
Whenever I see a beginner's guide to quantum theory, I always invariably see a phrase similar to:
"Stranger still, the electron doesn't even have properties like position and momentum until an observer measures them. "
And every time, I always think "define 'observe'", because that word is incredibly fluffy, vague as well as being immensely irritating. If a bat miles away happens to look in that direction with nothing in the way, is that counted as an observation? Are there a trillion different ways to observe it, and have they all been tried out to see the phenomenon stands? None, I repeat NONE of the articles I have ever read actually even remotely begins to touch upon that subject.
Why OpalCalc is the best Windows calc
When the article opened up with:
The more one probes the universe at smaller and smaller scales, the weirder matter and energy seem to behave
... I thought "patterns" (like in the Powers of 10 display at the science museum). I don't see why "they" are so surprised that the deeper you probe, the weirder it gets. It's natural - universal even! ... and I'll be taking the bus after that from now on.
I tried it on my bus driver this morning. Had a pleasant conversation, asked lots of questions
L'esperienza de questa dolce vita (The experience of this sweet life) - Dante Alighieri, The Divine Comedy
If anybody cares to read it, a preprint of the whole article can be found here.
Is it bad that I didn't even understand the summary?
The actual paper correctly says:
Non-locality can be exhibited when performing measurements on two or more distant quantum systems – the outcomes can be correlated in way that defies any local classical description. This is why we know that quantum theory will never by superceded by a local classical theory. Nevertheless, even quantum correlations are restricted to some extent – measurement results cannot be correlated so strongly that they would allow signalling between two distant systems.
Quantum entanglement (QE) provides a correlation not a communication. What this means is that not only can't you use QE to pass signals (or any information) between Alice and Bob, you actually need some other form of after-the-fact communication between them to detect the correlation in order to determine if QE happened at all. If QE was a method of communication then you could verify it by sending Bob a "cheat cheat" of what Alice was going to do or transmit. Instead, you need to look at the outcome of a series of measurements taken by Alice's and the outcome of a series of measurments taken by Bob just to see if QE actually happened.
Correlation is not communication.
We don't see the world as it is, we see it as we are.
-- Anais Nin
Let me guess... The "God" (Higgs Boson) particle is nothing more than nature's null value to assign properties of something without it actually existing. How would that be for irony?
I like to think of it as the particle (or system) being measured becoming classical-like during the measurement before going on its own merry quantum way again.
We don't see the world as it is, we see it as we are.
-- Anais Nin
I'm not a hacker, so I still don't get it. Can we get a car analogy, so we can all understand quantum physics?
Amazing that this hasn't shown up yet:
http://xkcd.com/817/
The alt text is very relevant: "A universe that needed someone to observe it in order to collapse it into existence would be a pretty sorry universe indeed."
The Higg's boson cannot exist until it is measured. Once it is ( in the LHC ) it will expand to the size of the universe in nothing flat, representing a force which will strip the characteristics from the particles leaving a universe which is super symmetric, has zero entropy, and is timeless. The Higg's field will then collapse, giving back the characteristics to the particles and the recycled universe will be reborn. Bob's your uncle.
Really? Locality? Maybe I'm missing something, but I'd say that the uncertainty principle is a pretty solid case for the existence of free will. That whole probabilistic universe thing is kinda antithetical to a deterministic universe.
I mean, with locality, venus isn't going to be influence my immediate actions, but if it's a deterministic universe, it doesn't really matter if it's the rest of the universe steering the boat, or if it's just my surroundings, the same things going to happen regardless. And spooky actions violate locality, but according to a paper, they do it in a probabilistic way, so I'm not quite seeing how locality is an argument for free will.
Care to explain? And go easy, I'm not really a physicist and don't have much patience for metaphysics.
Go grok the Butterfly Effect and you'll see how a probabilistic microscopic universe means that the macroscopic universe is also probabilistic.
Really, you're sounding like one of those people trying to make a distinction between micro and macro evolution. It's the same thing with the same mechanics. I mean, sure, it's a pretty safe bet that every atom in the sun won't decay overnight and the sun will indeed rise tomorrow. An astronomically good bet. But the fact that it's a bet at all means that it's not deterministic.
Unless you're arguing that a negligible chance isn't worth acknowledging, in which case I'd have to agree.
I have never been able to find a place to answer this idea: Is it possible that quantum entanglement is actually just fixing two particles to a stable spin?
(If I understand it correctly) If a person takes two entangled particles and take each one to a place farther than it takes the speed of light to travels, each can be measured faster than it would take for light to travel to "inform the other" of its state, yet each particle will always have the opposite of the other's state. The kicker for me is: one cannot know what state each will be, only that they will be opposites. This is why there is no information transfer. There is a correlation of behavior, not an inducement of behavior.
It seems to me this can be explained with the mind-experiment of replacing the two particles with a pair of coins. The two would naturally align and "stick," although in opposite directions, such as heads to heads or tails to tails. Quantum entanglement means the reduction of "noise" from space itself. If no longer being disturbed by interactions with the universe, physics would suggest they would continue to keep the the same momentum. If they are separated without being disturbed, distance is not relevant. Whenever, wherever, and as long as they are "viewed the same way" they will have opposite ends showing because they have kept the same rate of momentum. The catch is this is happening in more dimensions than our normal three, so the spin doesn't make sense in classical term.
P.S. I am an armchair physicist. I apologize for any misuse of a term.
Bel, the mostly sane.. "Of course I can't see anything! I'm standing on the shoulders of idiots." -- Me
You need to keep in mind that all of quantum mechanics is exclusively about probabilities, and no "reality" separate from the probabilities can exist. Niels Bohr repeatedly stated that quantum mechanics forbids any ontological questions to be raised; "is it real?" is simply not a question that this theory can answer. Unfortunately, people have been attempting to do just that ever since '37 and confused the issue beyond repair, because a quantum probability really is a purely epistemological quantity, describing what you believe about what you are measuring. When people start talking about "collapsing the wavefunction", they are confusing what happens in their mind with what happens in the real world, an error called the mind projection fallacy.
Before you make a measurement on the electron, you know nothing about it. In your mind, there is no information about its properties, so in your mind the electron does not exist (the definition of existence being that it has measurable properties) until you get some of that information. This does not mean that the electron does not exist in the real world, where it does indeed have all the properties that your experiment is about to measure.
Your mind does not have any definite information about the electron, but it does have a probability wavefunction for it. When you calculate a probability of something, you do so based on whatever prior information you have about it. For example, if you have measured the properties of other electrons before, you might make the assumption that the particular electron you are about to measure has a mass or charge similar to that of the other electrons, adjusted by the distribution of occurence of particular values. You know that all electrons have the same mass and charge, so our prior and posterior probability distributions (a graph of probability against measurement) are a single spike at the known value. Position and momentum, on the other hand, are unconstrained, so our prior probability distribution is a flat line infinitely close to zero. When you measure an electron's position or momentum, you are using that information to update your probability distribution into a single spike whose width is determined by the uncertainty of your measurement. You might view this update as a "collapsing" of your previous flat zero-knowledge distribution into this spike. A complete set of these probability distributions comprises the wavefunction of the electron, hence the term "wavefunction collapse".
It must be emphasized that this "collapse" happens entirely in your mind! While the electron's state may have been perturbed by your measurement, that has nothing do with it. The electron had a position before you measured it and still has one after you measured it. If you were to plot its position against the likelihood of finding it at that position, it would be a single spike at its real position with no uncertainty whatsoever. The uncertainty only occurs because you do not have perfect information about what the real position is, and it is only in the probability distribution in your mind does the spike have width.
It's the same with entanglement. You create two particles with correlated states, like say a production of an electron-positron pair. If you measure one particle and discover that it's an electron, you know for certain that the other one is a positron. All the ballihoo about "spooky action at a distance" is merely a mind projection fallacy; the second particle does not magically become a positron from nothing. It was a positron all along; you just didn't know that. When the probability wavefunction "collapsed" in your mind, you did not make any FTL measurements. The positron did not send you any information; you deduced it from w
Here is the paper, free access on arxiv as usual: http://arxiv.org/abs/1004.2507
There is no such thing.
If QE was a method of communication then you could verify it by sending Bob a "cheat cheat" of what Alice was going to do or transmit. Instead, you need to look at the outcome of a series of measurements taken by Alice's and the outcome of a series of measurments taken by Bob just to see if QE actually happened.
I think this was wrong. I believe that a cheat cheat of Alice's settings combined with Bob's settings and results is sufficient to see that QE occurred. The point is that you need an alternative form of communication between Bob and Alice just to verify QE. The cheat sheet serves as the alternative communications channel.
We don't see the world as it is, we see it as we are.
-- Anais Nin
and quantum computing is done for.
For justice, we must go to Don Corleone
From the Quantum Physics that I did at uni I would have thought that the relationship stated in the article was blindingly obvious, but then the way Scientists like to complicate Quantum Physics is one of the reasons I'm glad I never completed the degree in Applied Physics. They have the same problem lawyers do, the more complicated it sound the more important they feel.
Observation=physical interraction with a quanta enabling one to measure an eigen property of the wave function. For example in a case of entangled particle, it could be a photon, interracting with one of the particle, which enable you to find out in which state the entangled particle was, by measuring the resulting photon. Which is why that stupid film (can't remember the name) which was speaking of us human observing and influenciong the quantum world got it fully wrong. Our "looking" is fully passive (if you except the very few IR our body emit which don't enter the equation) and thus us wishing something CANNOT influence us getting it but the virtue of the "observer effect". they thought that observing=looking, but a better way to define it in physic is "observing=touching and changing".
It introduces a warp in the "surface" of the space-time continuum that particles with mass follow, much like setting a heavy object on a foam mattress will cause a depression in the foam.
Are you sure a particle has to have mass? I am not a physicist, but I was told that photons were massless.
"For I desired mercy, and not sacrifice" -- God
Wouldn't the whole branching universe idea break the laws of thermo dynamics. I mean it would require a constant supply of previously non-existent infinitely powerful energies to make all these new universes.
"For I desired mercy, and not sacrifice" -- God
Well, you could argue that within each universe, the laws of thermodynamics hold. There is no rule that says that if you have an infinite number of universes, the sum of the energy contained in each universe couldn't be infinite.
But remember, what we are discussing here are just interpretations and simple descriptions. Things like "spooky action at a distance" or "collapse of the wavefunction" are just meanings we attach to the formulas, it is not truth itself.
They have zero rest mass, but that changes as long as they are moving.
If he explores all forms and substances Straight homeward to their symbol-essences; He shall not die.